This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPP third generation partnership project
eNB evolved Node B
EUTRA evolved universal terrestrial radio access
LTE long term evolution
LTE-A LTE advanced
MME mobility management entity
OAM operation and maintenance
RSRP reference signal received power
SGW Serving Gateway
SON self-organizing network
TS technical specification
Tx transmit
UE user equipment
CDF cumulative distribution function
The specification of a communication system known as evolved UTRAN (EUTRAN, also referred to as UTRAN-LTE or as E-UTRA) is currently nearing completion within the 3GPP. One specification of interest is 3GPP TS 36.300, V8.8.0 (2009-04), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (EUTRA) and Evolved Universal Terrestrial Access Network (EUTRAN); Overall description; Stage 2 (Release 8), incorporated by reference herein in its entirety. Another specification of interest, in particular with respect to self-organizing networks, is 3GPP TR 36.902, V1.2.0 (2009-05), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (EUTRA) and Evolved Universal Terrestrial Access Network (EUTRAN); Self-configuring and self-optimizing network use cases and solutions (Release 9).
FIG. 1 reproduces FIG. 4.1 of 3GPP TS 36.300, and shows the overall architecture of the EUTRAN system (Rel-8). The EUTRAN system includes eNBs, providing the E-UTRA user plane and control plane (radio resource control) protocol terminations towards the UE. The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an S1 interface to an evolved packet core (EPC), more specifically to a mobility management entity (MME) by means of a S1-MME interface and to a serving gateway (SGW) by means of a S1-U interface. The S1 interface supports a many to many relationship between MMEs/Serving Gateways and eNBs.
The eNB hosts the following functions:
Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink (scheduling);
IP header compression and encryption of the user data stream;
selection of a MME at UE attachment;
routing of User Plane data towards Serving Gateway;
scheduling and transmission of paging messages (originated from the MME);
scheduling and transmission of broadcast information (originated from the MME or OAM (operation and maintenance)); and
measurement and measurement reporting configurations to provide mobility and scheduling.
Also of interest herein are the further releases of 3GPP LTE (e.g., LTE Rel-10) targeted towards future IMT-A systems, referred to herein for convenience simply as LTE-Advanced (LTE-A). Reference in this regard may be made to 3GPP TR 36.913, V8.0.1 (2009-03), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Requirements for Further Advancements for E-UTRA (LTE-Advanced) (Release 8), incorporated by reference herein in its entirety.
Previously power minimization has not been an important element to be considered during the network planning phase. Network planning in many cases is based on the assumption that all cells transmit at maximum power, even if transmitting with less than maximum power would lead to the same results.
Recently interest in energy savings has increased for a number of reasons. Typically, switching off cells which are not needed (e.g. during the night) is assumed to be the most relevant means to save energy. This approach, however, is not particularly advantageous, especially when there is some amount of communication traffic that must be accommodated.
Minimizing the transmit power of the cell offers a significant potential for energy savings, since the power is saved continuously, whereas switching off the cell can only be applied during times of low communication traffic.